Process for the manufacture of glycolic acid



the technical manufacture of the same.

UNITED STATES PATENT OFFICE.

OTTO LIEBKN-EGHT, OF FRANKFORT-ON-THE-MAIN, GERMANY, ASSIGNOR TO THE ROESSLER & HASSLAOHER CHEMICAL COMPANY, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK;

' PROCESS FOR THE MANUFACTURE OF GLYCOLIC ACID.

To all whom it nwby concern.-

Be it known that I, OTTO LIEBKNEOHT, a subject of the GermanEmperor, and a resident of Frankfort-on-the-Main, Germany, have invented a certain new and useful Process for the Manufacture of Glycolic Acid, of which the following is a specification.

This invention relates to an economical, easy, and effective process of manufacturing glycolic acid.

The processes heretofore practiced of manufacturing glycolic acid are not adapted for For instance, it is known that glycolic acid can be manufactured on a large scale from monochloracetic acid; but this process is notan easy one and is very expensive. As a further illustration, it is impossible to economically produce glycolic acid from oxalic acid and zinc-dust because the yield is poor and the zinc-dust very expensive.

I have discovered that oxalic acid in sul furic-acid or hydrochloric-acid solution is reduced electrolytically nearly quantitatively and with a very good current yield. In practicing my process I have found it most satisfactory in reducing the oxalic acid electrolytically to use electrodes having a high cathodic overvoltageas, for instance, lead electrodesand to use a diaphragm to separate the anodic and cathodic liquors. Both of these features are import ant, as well as the use of a not too dilute acid. An electrode not having a high cathodic overvoltage would give insufficient yields, and a too dilute acid would cause the oxalic acid, being highly ionized, to take too great a part in the conductivity of the current and to cause it to go to the anode, where it would be oxidized.

As an example illustrative of my process I give the following: Seven hundred parts of crystallized oxalic acid are dissolved in about three thousand three hundred parts of water and eleven hundred parts of thirty-per-cent. sulfuric acid are added while stirring. This solution forms a cathodic liquor, which it is of advantage to keep warm during the process of electrolyzation.

should be placed in the cathodic compartment of a suitable electrolytic apparatus provided with a suitable diaphragm, and the anodic liquor, comprising a thirty-per-cent. sulfuric acid, should be placed on the other Specification of Letters Patent. Application filed June 1A, 1906. Serial No. 321.669.

The cathodic liquor Patented Nov. 27, 1906.

side ofthe diaphragm. The density of the current at the cathode may vary greatly for instance, from twenty-five to two hundred and fifty amperes per square meter of surface of cathode. The presence of the diaphragm in connection with the use of a not too dilute acid largely prevents the anodic oxidation of the oxalic acid. On completion of the electrolysis the anodic solution may be used in preparing a fresh charge of the cathodic liquor.

It is preferable to stir the cathodic liquor during the electrolyzing, and, furthermore,

to add fresh acid in case the acid in the cathodic liquor becomes too weak, a too concentrated solution, however, being avoided at the cathode on account of the resulting low conductivity. It is advisable not to use sulfuric acid of a strength below fifteen parts concentrated sulfuric acid to one hundred parts of water, as otherwise the current yield and the nature of the product will be affected. The sulfuric acid can in the examples given be substituted for by about a twentypercent. hydrochloric acid. In place of lead electrodes carbon or graphite can be used; but in using carbon a proportionately larger amount of current will have to be provided. Besides this other undesirable reactions seem to take place simultaneously.

In order to produce glycolic acid from the electrolyzed solution in case sulfuric acid has been used, the solution is neutralized with lime, best added while stirring, until all the sulfuric acid and oxalic acid present is neutralized by the lime. In order to remove the last traces of sulfate of calcium, I use barium carbonate and oxalic acid in the usual way. In case hydrochloric acid has been used instead of the sulfuric acid during the electrolysis it is onlynecessary to evaporate the hydrochloric acid in order to get glycolic acid. The glycolic acid obtained by this process may be'used for technical as well as pharmaceutic purp oses.

As it is obvious that the process may be practiced in a number of different ways with considerable variation, I do not restrict my.- self to the steps or proportions described; but

What I claim, and desire to secure by Letters Patent of the United States, is

1. A process for the manufacture of glycolic acid from oxalic acid consisting in the electrolytic reduction of oxalicacid in the cathode-compartment of anelectrolytic app aratus in the presence-of electrodes having a cathodic overvoltag'e, the oxalic acid being dissolved in a suitable dilute acid kept Warm during the reduction and of such a degree of concentration that it excludes the oxalic acid from substantial participation in the conductivity.

2. A process for the manufacture ofglfycolic acid consisting in the electrolytic reduction of oxalic acid in the cathodecompartment of an electrolytic apparatusin the pres- 'ence of lead e1ectrodes,the oxalic acid being dissolved in a dilute sulfuric acid kept Warm 1 5 during the reduction and of such a degree of concentration that it excludes the oxalic acid from substantial participation in the conductivity.

In Witness whereof I have hereunto signed 20 my name in the presence of'tWo subscribing OTTO LIEBKNECHT.

Witnesses.

Witnesses HORST ZIEGLER," JEAN GRUND. 

